I'm trying to find a way to connect an external 3.5mm mic to my i9100 using a variable resistor (eg a volume controller in this case) to add impedance so that various mics with their different impedances can be connected freely, rather than just adding an inline resistor of arbitrary value.

and it says that impedance needs to be added in line with the mic so that the device recognises the mic as a mic (has to be above 1000 Ohms).

This has me wondering if, instead of adding a resistor in the cable that goes to the mic jack (or in the cable of the mic itself), it would be possible to use the splitting adapter above and plug a volume controller like the one below into the mic jack of the splitting adapter then the mic to the other end, like this: